The invention relates to an apparatus for actuating a throttle valve, secured to a throttle valve shaft, in internal combustion engines in particular in motor vehicles.
In such actuation apparatuses, the pivot lever is actuated by the driver via a pulley and a coupling link. Via a carrier, the pivot lever rotates the adjusting lever, which in turn pivots the throttle valve shaft and the throttle valve secured to it. To govern engine idling, the electromotive throttle valve adjuster acts upon the adjusting lever via a setting screw. In the resultant rotation of the adjusting lever the pivot lever is retained by the coupling link, and decoupling spring provides for a restoring force of the throttle valve counter to the servomotor. Since the working capacity of the servomotor is limited, the restoring force of the decoupling spring must not be excessively great. On the other hand, upon the return of the servomotor the restoring force must be sufficiently strong to assure both the restoration of the adjusting lever and switching, effected by the adjusting lever in its terminal position, of an actuation contact on the throttle valve adjuster.
In a known apparatus of the type described above, the decoupling spring is embodied for safety reasons as a symmetrical double spring, comprising two helical springs axially one behind the other, abutting one another at the face end and also abutting a radially offstanding annular flange of the spring guide sleeve, which is split in two transversely to the axial direction. One of the two sleeve parts of the spring guide sleeve is pressed axially against the adjusting lever. The two sleeve parts mesh with one another at the dividing line, so that the helical springs cannot become caught in the gap between the sleeve parts. If a wire of one helical spring should break, then the other helical spring still has sufficient restoring moment for the adjusting lever.
In this construction, the decoupling spring presses axially against the spring guide sleeve, and one sleeve part in turn presses against the adjusting lever. Upon rotation of the adjusting lever by the throttle valve adjuster, the result is relatively high friction between the stationary spring guide sleeve and the rotating adjusting lever and the end of the decoupling spring that rotates the adjusting lever. However, in the presence of such friction losses, the demand for a small actuating force of the adjusting lever counter to the restoring force of the decoupling spring, which is advantageous for the throttle valve adjuster servomotor, and the demand for sufficiently safe return of the adjusting lever by the decoupling spring upon the return of the servomotor, even if one of the two helical spring wires breaks, cannot be met.